The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawings will be provided by the Patent and Trademark Office upon request and payment of the necessary fee.
This invention relates to a microporous inkjet receptor that provides excellent images with pigmented inks deposited thereon in a manner that impedes migration of the pigmented inks when in contact with water.
Inkjet imaging techniques have become vastly popular in commercial and consumer applications. The ability to use a personal computer and desktop printer to print a color image on paper or other receptor media has extended from dye-based inks to pigment-based inks. The latter provide brilliant colors and more durable images because pigment particles are contained in a dispersion before being dispensed using a thermal inkjet print head, such as those commercially available from Hewlett Packard Corporation or LexMark Corporation in inkjet printers commercially available from Hewlett Packard Corporation, Encad Inc., Mimaki Corporation, and others.
Ink jet printers have been in general use for wide-format electronic printing for applications such as, engineering and architectural drawings. Because of the simplicity of operation, economy of ink jet printers, and improvements in ink technology the inkjet imaging process holds a superior growth potential promise for the printing industry to produce wide format, image on demand, presentation quality durable graphics.
The components of an ink jet system used for making graphics can be grouped into three major categories:
1 Computer, software, printer.
2 Ink.
3 Receptor sheet.
The computer, software, and printer will control the size, number and placement of the ink droplets and will transport the receptor film. The ink will contain the colorant or pigments which form the image and the receptor film provides the medium which accepts and holds the ink. The quality of the ink jet image is a function of the total system. However, the composition and interaction between the ink and receptor film is most important in an ink jet system.
Image quality is what the viewing public and paying customers will want and demand to see. Many other demands are also placed on the ink jet media/ink system from the print shop, such as rapid drying, humidity insensitivity, extended shelf life, waterfastness and overall handleability. Also, exposure to the environment can place additional demands on the media and ink (depending on the application of the graphic).
Porous membrane is a natural choice to use as an ink jet receptive media because the capillary action of the porous membrane can wick the ink into the pores much faster than the absorption mechanism of film forming water soluble coatings. However, in the past, when a porous coating or film has been employed to achieve desired quick dry, optical density has suffered greatly because the colorant penetrates too deep into the porous network. This type of problem is magnified by printers that dispense high volumes of ink per drop because extra film thickness may be required to hold all the ink. When the pore size and pore volume of the membrane are opened to allow the pigments to penetrate, the pigments can be stratified in the membrane. Meaning, the black, cyan, magenta, and yellow will be predominately found at different depths depending on the order of application. Hence, some of the first color(s) applied is /are optically trapped in the image by subsequent application of other pigmented ink. Furthermore, lateral diffusion of the ink can also be a problem inherent in porous membranes used as receptive media. When pigmented inks are jetted onto a porous film that has a pore size that is too small, color pigments will be filtered on the top of the membrane rendering high image density, but the pigments could easily smear and have the effect of never drying. Also, excess fluid from the ink can coalesce, or even worse, pool and run on the image before the water/glycol carrier is wicked away.
The chemical formulation of the pigmented inkjet ink has considerable complexity due to the requirement of continued dispersion of the pigment particles in the remainder of the ink and during jetting of the ink.
The typical consumer medium for receiving dye-based inkjet inks has been paper or specially coated papers. However, with too much inkjet ink in a given area of the paper, one can see the over-saturation of the paper with the aqueous ink in which dye was dissolved.
As inkjet inks have become more commercially oriented and pigmented-based inks have become more prevalent, different media have been tried in an attempt to control the management of fluids in the ink.
Japanese Patent JP 61-041585 discloses a method for producing printing material using a ratio of PVA/PVP. The disadvantage is inadequate waterfastness and wet rub off properties.
Japanese Patent JP61-261089 discloses a transparent material with cationic conductive resin in addition to a mixture of PVA/PVP. The material is water fast and smudge proof but the wet rub off properties are poor.
European Patent Publication EP 0 716 931 Al discloses a system using a dye capable of co-ordinate bonding with a metal ion in two or more positions. Again binder resins are used with inorganic pigments in the paper or film. The metal ion was preferred to be jetted on before imaging and additional heating is necessary to complete the reaction. This system was not claiming to be water fast; the focus was long term storage without fading from heat or light.
U.S. Pat. No. 5,537,137 discloses a system to achieve waterfastness by curing with heat or UV light. In the body of the patent, examples of their coatings contained Ca++ from CaCl2. This was added to provide reactive species for the acid groups on the dispersed polymer. The coating remains water soluble until UV or heat curing after imaging.
Hence, the current special ink jet media employ vehicle absorptive components, and sometimes optional additives to bind the inks to the media. As a consequence current media are inherently moisture sensitive and can be fragile to handling and subject to finger smearing. Moreover, the vehicle absorptive components usually consist of water soluble (or swelling) polymers which result in slower printing speeds and dry times.
Pigmented ink delivery systems have also dealt with pigment management systems, wherein the resting location of the pigment particles are managed to provide the best possible image graphic. For example, U.S. Pat. No. 5,747,148 (Warner et al.), discloses a pigment management system in which a suitable supporting layer (including in a listing a microporous layer) has a two layer fluid management system: a protective penetrant layer and a receptor layer, both layers containing filler particles to provide two different types of protrusions from the uppermost protective penetrant layer. Electron microphotographs in that application show how the pigment particles of the ink encounter smooth protrusions that provide a suitable topography for pigment particle xe2x80x9cnestingxe2x80x9d and rocky protrusions that assist in media handling and the like.
Other ink receptors have been disclosed, including U.S. Pat. Nos. 5,342,688 (Kitchin); 5,389,723 and 4,935,307 (both Iqbal et al.); 5,208,092 (Iqbal) 5,302,437 (Idei et al); U.S. Pat. No. 5,206,071 (Atherton et al.); and EPO Patent Publication 0 484 016 A1.
One prior activity has combined a fluid management system with a pigment management system, as disclosed herein and in copending, coassigned, U.S. patent application Ser. No. 08/892,902, the disclosure of which is incorporated herein by reference. This work solves the need for an inkjet receptor to have both a pigment management system for flocculating or agglomerating incoming pigment/dispersant particles and a fluid management system for efficiently dispensing with the carrier fluids within a porous substrate.
It has been found that inkjet receptor media require durability for exposure to water in the form of humidity, rain, dew, snow, and the like.
It has also been found that pigment particles in aqueous inkjet ink formulations require time to establish a stable relationship with the medium upon which they have been deposited during inkjet printing.
It has been found that pigment particles are capable of migration within pores of a porous inkjet receptor medium, even if such receptor medium has both a fluid management system and a pigment management system.
What the art needs is an inkjet receptor medium that assures rapid establishment of a stable relationship between pigment particles (and their dispersants) and the inkjet receptor medium, particularly when the printed medium is likely to be exposed to water or other solvents shortly after printing.
One aspect of the present invention is a migration inhibitor for pigmented inks comprising a copolymer of at least two different hydrophilic monomers, each of whose homopolymers are hydrophilic yet the resulting copolymer from the different hydrophilic monomers is sparingly soluble in water.
For purposes of this application, xe2x80x9csoluble in waterxe2x80x9d means dissolution of the monomer or polymer in deionized water at room temperature (about 15-18xc2x0 C.) at a rate of 50-90 grams/100 g of water. By contrast, xe2x80x9csparingly soluble in waterxe2x80x9d means the monomer or polymer is capable of being dispersed in deionized water at room temperature (about 15-18xc2x0 C.) without becoming substantially dissolved (no more than about 1 gram/100 grams of water) in that deionized water, notwithstanding possible solubility in blends of water and other hydrophilic solvents.
One feature of the present invention is a homopolymer or copolymer that has hydrophilic interaction sites for both pigmented particles and their associated dispersants and hydrophilic interaction sites for multivalent metal ion coordination. xe2x80x9cHydrophilic interactionxe2x80x9d in the present context means a physicochemical phenomenon whereby the functional group(s) in the homopolymer or copolymer undergoes interactions with the dispersants and the metal ions in hydrophilic medium.
One advantage of the present invention is that a dispersible-co-soluble hydrophilic copolymer or hydrophilic homopolymer of the present invention can substantially immobilize pigment particles and their associated dispersants from migration when the printed inkjet receptor medium comes in contact with water.